This invention relates to a method and product for water quality management for aquaculturists. More specifically, the invention relates to the simultaneous removal of chloramines, chlorine and ammonia which are toxic to aquatic life.
The culture of aquatic organisms, also known as aquaculture, in the U.S. and elsewhere for food, recreation, education, research, and hobby purposes is a fast growing industry. The world production from 1971 to 1978 of fishes, crustaceans and molluscs raised for food exceeded 10 million pounds. In the U.S. alone these same species exceeded 184 million pounds in 1980 If nonfood baitfish and aquarium species were added to the U.S. production in 1980, then aquacultured animals would represent more than 206 million pounds This translates into a total commercial value of over 210 million dollars In short, aquaculture is big business and its growth continues at a significant rate. The profit potential in aquaculture has created such incentives that its many enterprises and operations quickly outdistance the supporting sciences and technologies This results, not only in production losses and failure to meet product demands, but also in heavy financial losses.
Two areas in particular stand out as sources of frustration and lost profits for aquaculturists. These are disease management and water quality management. Although the present invention is particularly related to water quality management, it should be noted that chemotherapeutic treatmert for disease management is enhanced when high standards of water quality are maintained.
With fishes and other aquatic animals, just as with other animals and humans, if a proper, non-stressful environment is provided then the incidence of disease conditions is all but eliminated. Two major types of systems exist for raising aquatic life. These are closed and open systems. There are two types of closed systems; the closed, recirculating system, and the closed, non-recirculating system. The closed, recirculating system, such as a home aquarium, is characterized by a fixed volume of water which is continuously or intermittently circulated through a fish holding tank. The closed, non-recirculating system, such as a farm pond, is characterized by a fixed volume (usually greater than in the previous example) of water to which fresh makeup water is added, as needed, such as for compensation for evaporation. In a non-recirculating, flow-through system, such as a raceway used to raise trout, fresh makeup water is continuously fed to the fish holding structure while a like quantity of water is continuously withdrawn from the structure. The water environment of the closed, recirculating system can be controlled with intensive care and maintenance. The water quality of a closed, non-recirculating system is very difficult to control except by more or less natural means (i.e., photosynthetic process to provide oxygen and bacterial processes to convert toxic wastes). The non-recirculating, flow-through water systems often have problems similar to closed systems, but environmental control in flow-through systems is generally as difficult as in closed non-recirculating systems. In either system, the objective of successful water quality management is the removal or neutralization of toxic substances which stress cultured aquatic life forms and thereby to add significantly to the production and profitability of aquaculture.
Among the many compounds found in natural, waste and potable waters which are toxic to aquatic organisms, ammonia (NH.sub.3), chlorine in the form of hypochlorus acid (HOCl) and hypochlorites (OCl.sup.-), and chloramines (NH.sub.2 Cl, NHCl.sub.2) are among the most toxic and ubiquitous.
Ammonia is present in natural waters as a result of animal metabolism of proteins; urinary, fecal and respiratory wastes; and bacterial mineralization of nitrogenous bases. This means that the aquatic organisms (fishes, crustaceans, molluscs, etc.) themselves contribute significant, toxic pollutants to their own water. In waste water these same sources, as well as technological wastes, account for ammonia presence. Ammonia in potable water is due to the failure to remove it in the purification process or due to the purposeful addition for quality control. In a review of management practices, researcher Stephen Spotte (Fish and invertebrate culture, John Wiley & Sons, New York, 1979) observed that current evidence indicates that NH.sub.3 is significantly more toxic than its ionic form, NH.sub.4.sup.+ (ammonium). Even if this were not true, to attempt to control the factors such as pH, temperature and salinity that effect the NH.sub.3 :NH.sub.4.sup.+ ratio could be more harmful and costly. Spotte suggested that management techniques be targeted to remove as many sources of ammonia as possible from the culture water such as uneaten food, dead animals and plants and to keep the densities of cultured species moderate and to not allow the total ammonia level to exceed 0.13 ppm (0.13 mg NH.sub.4.sup.+ per liter of culture water). The problem with Spotte's suggestions is that for commercial aquaculturists moderate densities of cultured animals are seldom profitable and for aquarium hobbyists there is always room for one more fish in an already overcrowded aquarium.
Other respected researchers have warned of the dangers of ammonia in aquaculture. The safe level for salmonids such as trout and salmon is considered to be from 0.005 to 0.02 ppm. As a predisposing factor in bacterial gill disease of cultured food fishes, ammonia levels over 0.3 ppm are considered dangerous.
When the foregoing standards for water quality are compared to ammonia levels which can be encountered in both culture water and natural waters, the serious nature of this problem can be better appreciated. The ammonia levels in wastewater can range up to and over 5000 ppm. In aquarium and aquaculture systems it is not unusual to encounter total ammonia concentrations of between 1.0 and 3.0 ppm.
Another fish threatening substance is chlorine. Chlorine is most often present in water as a result of disinfection processes. It is not found in natural waters unless there has been contamination from wastewater or potable water sources. Aquaculturists and aquarists simply have no direct control over the quantity of chlorine, or associated chloramines, introduced to municipal water supplies. However, no matter what the initial concentration of chlorine, or chloramines, it must be reduced to zero before any water in which it is present can be safely used for culture purposes. Levels of chlorine from 0.2 to 0.3 ppm are rapidly toxic to fishes. The U.S. Environmental Protection Agency recommends an upper level of 0.003 ppm for continuous exposure by coldwater and warmwater fishes. Chlorine levels in municipal water supplies range up to 2.5 ppm. When used as a disinfectant agent for cleaning aquariums, the recommended solution typically contains 50 ppm chlorine. Accordingly, the aquarium must be very thoroughly rinsed to remove any trace of the chlorine after cleaning.
Chloramines are most often present in water for the same reasons as the presence of chlorine. However, some chloramines in natural and waste waters result from the chemical combination of chlorine with the ammonia normally found in these waters. The chloramine level in a given water can range quite high to over 5000 ppm, but the levels encountered in most municipal tap waters is in the range of 0.5 to 4.0 ppm. Even the latter range represents a deadly concentration level for aquatic life.
The reduction in concentrations of these toxic components in water, when their initial introduction cannot be controlled, is crucial in the culture, maintenance and display of freshwater, brackish water (estuarine), and marine organisms. In addition, the timely reduction in concentrations of these toxic components is also desirable.
In the case of chlorine a process of reductive dechlorination is most often practiced. However, granular activated carbon is also used as a chemical adsorbant to remove chlorine from water. Ammonia removal can be accomplished by adsorption on zeolites like clinoptilolite and phillipsite and by bacterial nitrification. The efficiencies of these two processes are effected by contact time (i.e., how long the water is in contact with the adsorbant or bacterial bed) and other conditions such as temperature, dissolved oxygen levels, the presence of interferring substances (i.e., certain antibiotics in the case of nitrifying bacterial beds, and highly surface active organics in the case of chemical adsorbants), and maintenance procedures (i.e., cleaning routines) of the filters themselves. Chloramines can be removed by reductive dechlorination followed by adsorption or nitrification of the freed ammonia.
Dechlorination has been shown to be a highly reliable process and one which works well under most conditions found in culture water, the term referring to the water used to maintain, grow or breed aquatic plants and animals. One problem with this process presents itself when thiosulfates, S.sub.2 O.sub.3 -(the substances used in the majority of commercially available dechlorinators), are used; excess thiosulfate ion reacts with dissolved oxygen in water and inadvertent or purposeful overdosing can result in a reduction of dissolved oxygen in culture water which can in turn cause respiratory stress in the cultured organisms. In addition, many commercially available dechlorinators have been found to be inadequate for complete dechlorination of even relatively lightly chlorinated (i.e., less than 4.0 ppm total chlorine) potable waters. The use of granular activated carbon has been common and is most often employed in laboratories for the preparation of chlorine-free culture water. Nevertheless, a recent study details the problems associated with using granular activated carbon alone as a method of dechlorinating water for aquatic toxicological studies. Stephen J. Mitchell and Joseph J. Cech, Jr., 1983, "Ammonia-caused gill damage in channel catfish (Ictalurus punctatus): confounding effects of residual chlorine", Can. J., Fish. Aquat. Sci., 40(2), pp. 242-247.
The elimination of chloramines (i.e., dechloramination) from water used for culture purposes has reached more creative levels. One method currently used is to dechlorinate with the usual dechlorinators then remove the freed ammonia by adsorption on granular clinoptilolite placed in a filtering device or by addition the finely divided, powder, clinoptilolite directly to the water. In actuality, most dechloramination is achieved by dechlorinating in the usual way and allowing the ammonia to be oxidized by nitrifying bacteria. Just as with chlorine, granular activated carbon has been used to remove chloramines from water, but this process has also been questioned by the Mitchell and Cech study in 1983. The same study showed that partial dechlorination allowed the residual chlorine to potentiate the toxic effects of ammonia on fish.
The removal of ammonia released into water when chloramines are dechlorinated is likewise problematical. Biological filtration is a process of bacterial conversion or nitrification of toxic ammonia and nitrite ions (NO.sub.2.sup.-) to less toxic nitrate ions (NO.sub.3.sup.-). Biological filtration, however, is easily interrupted and inhibited, and the intermediate product, nitrite ions (NO.sub.2.sup.-), is significantly more toxic to aquatic organisms than the precursor ammonia. Until a biological filter bed is fully conditioned and properly functioning (an average of 21 days), there is a constant increase in the concentration of the nitrite ions until the precursor ammonia is reduced below its inhibiting (to the nitrite converting Nitrobacter species of bacteria) concentrations.
The removal of ammonia by adsorption has its own set of problems. Among these are flow rate and contact time, adsorbant grain size, temperature, adsorbant capacity, and the concentration of interfering ions such as sodium (Na.sup.+) and potassium (K.sup.+). Clinoptilolite has approximately 5% of the capacity in salt water that it exhibits in freshwater and, therefore, correspondingly larger quantities of this adsorbant are required for a salt water application.
Commercial products do currently exist which claim to remove or neutralize one or more of the toxic substances chlorine, chloramines and ammonia. However, they all suffer from one or more of the above described shortcomings. Simple dechlorinators, if properly dosed will completely neutralize chlorine. These same dechlorinators will break the chlorine-ammonia bonds in chloramines and neutralize the chlorine but will not neutralize the freed ammonia. Ammonia adsorbants, if used properly will adsorb and remove ammonia from water, but will have no effect upon any chlorine present and they will not function properly in saline waters. Biological filters will maintain ammonia concentrations at low levels, even in saline waters, but they require a long start-up time (up to 21 days), are slow to react to increased ammonia loads, and require a relatively narrow range of operating conditions. Products which are combinations of dechlorinators and ammonia adsorbants will not function in saline waters and cause a temporary cloudiness in the treated water due to the dispersion of the finely divided adsorbant.
Accordingly, aquaculture needs a safe and effective way to remove chloramines, chlorine and ammonia which overcomes the limitations, dangers and shortcomings of the various techniques presently employed. The primary goal of this invention is to fulfill this need in the industry.
More specifically, an object of the invention is to provide a product and method for the removal of chloramines, chlorine and ammonia which, unlike existing zeolites and ion-exchange resins, functions as well in saline water as it does in freshwater treatment.
Another object of the invention is to provide a completely safe product and method for the removal of chlorine, chloramine and ammonia which is non-toxic to fishes, aquatic invertebrates, marine and freshwater algaes, and aquatic plants.
Another object of the invention is to provide a product and method for the removal of chloramines, chlorine and ammonia which does not cause clouding in hard or soft water or in salt water as do products which contain insoluble zeolites.
Yet another object of the invention is to provide a product and method for the removal of chloramines, chlorine and ammonia in which the time required for neutralization is greatly reduced from the time required by earlier techniques. With this invention, neutralization times vary from one to five minutes for "free" chlorine (hypochlorites), ten to thirty minutes for chloramines ("combined" chlorine), and twelve minutes to one hour for free ammonia.
An additional object of the invention is to provide a product and method for the removal of chloramines, chlorine and ammonia which does not react with dissolved oxygen in either freshwaters or saline waters.
Another object of the invention is to provide a product and method for the removal of chloramines, chlorine and ammonia which is not pH dependent and functions equally well throughout the "normal" pH range, 5.0 to 9.0, of waters in which most aquatic life is found.
Another object of the invention is to provide a product and method for the removal of chloramines, chlorine and ammonia which is largely uninhibited by the presence of commonly used antibiotics such as chloramphenicol, nitrofurans, and sulfa drugs, or by the presence of antiparsiticals such as copper sulfate, metronidazole and formaldehyde.
A further object of the invention is to provide a product and method for the removal of chloramines, chlorine and ammonia which can be combined with water conditioning chemicals such as other dechlorinators, electrolyte mixes, and trace element mixes.
Yet a further object of the invention is to provide a product and method of the character described which is safe, reliable and economical to effect removal of chloramines, chlorine and ammonia.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description of the invention.